This invention relates to a tool for cutting subterranean roots while digging a root ball for transplanting a tree, shrub or other plant, and more particularly, to a tool for cutting roots located beneath the center of an area to be excavated in forming a root ball for transplanting a tree, shrub or other plant.
Digging and transplanting trees and shrubs which have been grown in the ground (generally referred to as field-grown stock to distinguish from container-grown stock) is an important part of the nursery and landscaping business. Field-grown trees and shrubs, whether growing in a nursery or elsewhere, are generally transplanted to another location using either the bare root technique or the balled and burlapped ("B&B") technique. The tool of the invention may be useful in practicing the bare root technique, but is particularly useful in practicing the B&B technique.
In transplanting trees and shrubs using the bare root technique, the root system of the plant to be transplanted is isolated and the soil around those roots is loosened by digging around the plant with a hand spade or the like. The plant is then removed from the ground and the soil is removed from the root system. The plant with its bare root system may then be transplanted. The bare root technique is generally appropriate only for small, dormant deciduous trees and shrubs up to about 6 feet tall or small, dormant evergreens up to about 1 foot tall. While this technique has the advantage of producing specimens for transplanting that are relatively light and easy to handle, it is generally not an appropriate technique for many plants, especially the larger trees and shrubs, that a nurseryman or landscaper may want to transplant.
Trees and shrubs of relatively large size are generally transplanted along with a root ball made of the roots of the plant extending for some distance from the base of the trunk, and the soil surrounding those roots. This excavated volume of roots and soil is generally referred to as a root ball. For handling during transplanting, the root ball may be lifted from the ground and then groomed to trim the projecting roots at the periphery of the root ball and to remove excess soil. The resultant root ball is generally wrapped in burlap or other similar material to protect the root ball. Thus, this method of digging and transplanting trees and shrubs is referred to as the balled and burlap method or "B&B" method. It is sometimes the case, especially when the tree or shrub is replanted immediately after digging to a nearby location, that plant may be transplanted directly without wrapping the root ball in burlap. For purposes of this application, however, if a significant root ball is dug and transplanted, the method is still referred to as the B&B method even though the root ball is not wrapped in burlap. Although a seemingly simple process, careful and successful transplantation by the B&B technique may be time consuming and quite arduous if done using tools available in the prior art.
The first task of the nurseryman is proper sizing of the root ball. The roots of trees and shrubs typically radiate outward and downward from the crown (the point where the trunk and roots meet). Tree and shrub roots tend to be concentrated near the ground surface; even large trees have most of their roots within the upper 16 inches of soil. Many trees and shrubs, however, will also have some major roots which extend deeply downward from the crown to gather nutrients and water from the lower levels in the soil and serve the important purpose of helping to anchor the plant securely.
Before digging a tree or shrub it is necessary to determine how large a portion of the root systems needs to be dug. The root ball (the soil containing the portion of the root system which will be kept with the tree or shrub) is usually roughly upside-down hemispherical in shape, and centered around the base of the trunk of the tree or shrub. The depth of the root ball is generally not more than half its diameter and may be less. The root ball is generally 10 to 12 times the diameter of the trunk of the tree or shrub as measured just above the basal flair of the trunk. A tree or shrub dug with a root ball of this size will generally transplant satisfactorily and avoid undue transplant shock.
In order to enhance the quality and viability of the root ball, a technique known as root pruning is often employed. A dense, compact root system concentrated near the crown is highly desirable for stock which is to be transplanted. Including a relatively large portion of the root system in the root ball will enhance the viability of the tree or shrub to withstand the stress of transplanting and will effectively knit the root ball together making a mechanically solid root ball which is relatively more likely to remain intact during transplanting. This later characteristic is important since fracturing of crumbling of the root ball is likely to damage the root system within it.
Root pruning is a procedure which can help trees and shrub develop a dense, compact root system concentrated near the crown. In root pruning, roots which extend beyond the circumference of the area which is to be the root ball are cut while leaving the plant in the ground. Trees and shrubs typically respond to root pruning by growing an abundance of new, fine, roots extending from the remaining roots within the root ball. To gain the benefit of root pruning, sufficient time should be allowed between root pruning and transplanting for the growth of the new roots to occur. The length of this time varies depending upon a variety of factors such as soil temperature and the size and kind of tree or shrub involved. Significant root regrowth can occur within a little as a week after pruning. However, it is often desirable to allow a much longer period of time, even as much as one year or more, between root pruning and transplanting.
Root pruning may occur in two steps to avoid undue damage to the overall root system of a tree or shrub. Initially, about 2/3 to 3/4 of the circumference of the root ball can be root pruned. After allowing some time for the root system to recover, the remainder of the root ball can be pruned. Root pruning in two stages is most advisable when dealing with larger sizes of trees or shrubs, or with kinds of trees or shrubs which are difficult to transplant. Properly executed, root pruning encourages the development of dense, compact root systems, even in species of plants which naturally tend to have diffuse root systems.
Although, as stated above, the root ball at the surface is generally 10 to 12 times the diameter of the trunk, it is a good idea to root prune a somewhat smaller ball, generally around a circumference of only 8 to 10 times the diameter of the trunk. Doing so reduces the loss of fine new roots which develop near the periphery of the root ball following root pruning.
The tools currently available to the nurseryman in transplanting a tree or shrub by the B&B technique include a nursery spade, and certain mechanical devices such as a U-blade type digger and a multiple blade type digger. A U-blade type digger has a single large blade in the shape of a bucket or scoop with a forward edge in the shape of a "U" or a "V." The blade is mounted on a tractor, backhoe, or similar device. In use, the blade is positioned so that the forward edge of the blade is pointed down into the ground just outside the outline of the root ball to be dug. The blade is then driven down into the ground and simultaneously rotated under the plant so that it essentially scoops the root ball into the blade.
A multiple blade type digger is also mounted on a tractor, backhoe or similar device. It has two or more, usually triangular, broad blades that may be positioned around the outline of a root ball to be dug and angled towards the center of the plant. The blades are mechanically driven downward into the ground so that they meet under the plant and essentially enclose the root ball within the blades.
Root Pruning
Prior to the invention, root pruning, the advantages of which are described above, was generally accomplished using a nursery spade. Nursery spades are designed so their blades penetrate the soil readily and generally have a straight leading edge which tends to slice through roots which it encounters rather than pushing them aside.
One way to root prune a tree or shrub with a spade is to insert the spade, angled at about 20 to 35.degree. from the vertical into the ground in a circular path around the plant. The spade is inserted to the full depth of the blade. Care should be taken to overlap successive strokes of the blade slightly so that all the roots within reach of the spade are cut. While the blade is fully inserted, the handle may be pushed downwards slightly until the root ball shows a bit of movement. For small root balls (less than 18 inches in diameter), the root ball can often be broken completely free of the surrounding soil in this way. As the root ball diameter increases over approximately 18 inches, however, the difficulty of breaking the roots which extend downward from the center of the plant increases markedly. For such root balls, the roots at the center are likely to remain intact.
Except in the case of very small root balls as described above, when the procedure described in the preceding paragraph is used the root ball is only partially root pruned and the benefits of root pruning are only partially realized. Also, where uncut roots remain after pruning, when the root ball is torn free by prying with a spade for transplanting, the force required often causes the root ball to crumble and the roots to be torn rather than cut cleanly. Such torn roots often heal more slowly than cleanly cut roots, and are more subject to invasion by disease organisms.
Another approach to root pruning with the spade is to dig a trench around the prospective root ball to a depth of about 2/3 the depth of the root ball. Once the trench has been dug, the spade may be positioned at the inner bottom corner of the trench and angled at 40 to 60.degree. from the vertical. It may then be inserted and the process repeated around the fall circumference of the root ball to effectively cut all of the roots extending downward from the plant. The larger the proposed root ball, the wider and deeper the trench will need to be in order to properly prune the root ball. Properly executed, this procedure results in a neat, thorough job of root pruning, but is very laborious and time consuming and requires a large volume of soil, often greater than the volume of the root ball itself, to be removed.
Root pruning to some extent may also be achieved using the mechanical devices described above, the U-blade type digger and the multiple blade type digger. Using a U-blade digger, it is usually best to insert the blade twice, once each from directions close to 180.degree. apart. This requires that access to the tree or shrub be unusually good so that the tractor, backhoe or similar device can have access to the plant from both of two opposite sides. Furthermore, the U-blade has a broad, relatively dull, slow moving blade that tends to encounter a number of roots simultaneously and to tear or mangle them rather than cutting them cleanly. Consequently, it generally does a rather ragged job of cutting the roots. As a result, even when transplanting with a U-blade type digger, it is often desirable or necessary to perform the root pruning using a nursery spade.
Multiple blade type diggers can also be used for root pruning. This is done by inserting the blades under the plant to cut the roots and then removing the blades without lifting the plant. However, as with the U-blade diggers, a multiple blade type digger tends to push and tear roots rather than cutting them cleanly. Additionally, multiple blade type diggers are complicated and expensive; in sizes suited to larger root balls they are very expensive. Multiple blade type diggers do not cope well with obstacles such as stones in the soil and may fail to cut roots on the lowest part of the root ball. As with the U-blade type diggers, it is also necessary to have access to the plant by the rather large and cumbersome mechanical equipment necessary for operation of the multiple blade type diggers.
Digging for Transplanting
With or without prior root pruning, trees and shrubs must be dug from the ground if they are to be transplanted. Prior to the invention, this was often done using a nursery spade. The nursery spade is used to separate the root ball, which is generally larger than the volume defined by root pruning, from the surrounding soil. Unless a small root ball is being dug, this requires digging the soil from around and under the plant to expose most of the periphery of the root ball for wrapping. If the root ball is relatively large, mechanical means may be necessary to lift the root ball even after it has been prepared by digging with a nursery spade.
Alternatively, a U-blade type digger may be used to finish digging and lifting the plant. As described above, the bucket or scoop is positioned outside the root ball defined by root pruning with the forward edge of the blade pointed down into the ground. The blade is then driven down into the ground and simultaneously rotated under the plant so that it essentially scoops the root ball into the bucket formed by the blade. The bucket with the root ball in it may be mechanically lifted out of the ground, deposited on material such as burlap for wrapping, or moved directly to the chosen location for transplanting.
In multiple blade type diggers, the two or more triangular blades are positioned around the diameter of the root ball, generally outside the volume defined by root pruning, and angled inward. The blades are then driven into the ground so that they meet beneath the center of the tree or shrub. The blades may be mechanically interlocked to strengthen the rigid container formed when they are in place under the root ball. The root ball and plant may then be lifted up and out of the ground by the power supplied by, for example, tractor mounted hydraulic equipment.